In addition to their known uses in diagnostics, antibodies have been shown to be useful as therapeutic agents. For example, immunotherapy, or the use of antibodies for therapeutic purposes has been used in recent years to treat disease and cancer. Immunotherapy can be passive or active.
Passive immunotherapy involves the use of monoclonal antibodies in cancer treatments. See for example, Cancer: Principles and Practice of Oncology, 6th Edition (2001) Chapt. 20 pp. 495-508. These antibodies can have inherent therapeutic biological activity both by direct inhibition of diseased or tumor cell growth or survival and by their ability to recruit the natural cell killing activity of the body's immune system. These agents can be administered alone or in conjunction with radiation or chemotherapeutic agents. Rituximab and Trastuzumab, approved for treatment of non-Hodgkin's lymphoma and breast cancer, respectively, are two examples of such therapeutics. Alternatively, antibodies can be used to make antibody conjugates where the antibody is linked to a toxic agent and directs that agent to the tumor by specifically binding to the tumor. Gemtuzumab ozogamicin is an example of an approved antibody conjugate used for the treatment of leukemia. Monoclonal antibodies that bind to cancer cells and have potential uses for diagnosis and therapy have been disclosed in publications. See, for example, the following patent applications which disclose, inter alia, some molecular weights of target proteins: U.S. Pat. No. 6,054,561 (200 KD c-erbB-2 (Her2), and other unidentified antigens 40-200 KD in size) and U.S. Pat. No. 5,656,444 (50 KD and 55 KD, oncofetal protein). Examples of antibodies in clinical trials and/or approved treatments of solid tumors include: Trastuzumab (antigen: 180 kD, HER2/neu), Edrecolomab (antigen: 40-50 kD, Ep-CAM), Anti-human milk fat globules (HMFG1) (antigen>200 kD, HMW Mucin), Cetuximab (antigens: 150 kD and 170 kD, EGF receptor, Alemtuzumab (antigen: 21-28 kD, CD52), and Rituximab (antigen: 35 kD, CD20).
The antigen targets of trastuzumab (Her-2 receptor), which is used to treat breast cancer, and cetuximab (EGF receptor), which is in clinical trials for the treatment of several cancers, are present at some detectable level on a large number of normal human adult tissues including skin, colon, lung, ovary, liver, and pancreas. The margin of safety in using these therapeutics is possibly provided by the difference in the level of expression or in access of or activity of the antibody at these sites.
Another type of immunotherapy is active immunotherapy, or vaccination, with an antigen present on a specific pathogen, diseased cell or cancer, or a DNA construct that directs the expression of the antigen, which then evokes the immune response in the individual, ie., to induce the individual to actively produce antibodies against their own disease, pathogen or cancer. Active immunization has not been used as often as passive immunotherapy or immunotoxins.
Several models of disease (including cancer) progression have been suggested. Theories range from causation by a single infective/transforming event to the evolution of an increasingly “disease-like” or “cancer-like” tissue type leading ultimately to one with fully pathogenic or malignant capability. Some argue that with cancer, for example, a single mutational event is sufficient to cause malignancy, while others argue that subsequent alterations are also necessary. Some others have suggested that increasing mutational load and tumor grade are necessary for both initiation as well as progression of neoplasia via a continuum of mutation-selection events at the cellular level. Some cancer targets are found only in tumor tissues, while others are present in normal tissues and are up-regulated and/or over-expressed in tumor tissues. In such situations, some researchers have suggested that the over-expression is linked to the acquisition of malignancy, while others suggest that the over-expression is merely a marker of a trend along a path to an increasing disease state.
An ideal diagnostic and/or therapeutic antibody would be specific for an antigen present on a large number of diseased cells or cancers, but absent or present only at low levels on any normal tissue. The discovery, characterization, and isolation of a novel antigen that is specifically associated with disease(s) or cancer(s) would be useful in many ways. First, the antigen could be used to make monoclonal antibodies against the antigen. An antibody would ideally have biological activity against diseased or cancer cells and be able to recruit the immune system's response to foreign antigens. An antibody could be administered as a therapeutic alone or in combination with current treatments or used to prepare immunoconjugates linked to toxic agents. An antibody with the same specificity but with low or no biological activity when administered alone could also be useful in that an antibody could be used to prepare an immunoconjugate with a radio-isotope, a toxin, or a chemotherapeutic agent or liposome containing a chemotherapeutic agent, with the conjugated form being biologically active by virtue of the antibody directing the toxin to the antigen-containing cells.
One aspect desirable for an ideal diagnostic and/or therapeutic antibody is the discovery and characterization of an antigen that is associated with a variety of cancers. There are few antigens that are expressed on a number of types of cancer (e.g., “pan-cancer” antigen) that have limited expression on non-cancerous cells. The isolation and purification of such an antigen would be useful for making antibodies (e.g., diagnostic or therapeutic) targeting the antigen. An antibody binding to the “pan-cancer” antigen could be able to target a variety of cancers found in different tissues in contrast to an antibody against an antigen associated with only one specific type of cancer. The antigen would also be useful for drug discovery (e.g., small molecules) and for further characterization of cellular regulation, growth, and differentiation.
What is needed are novel targets on the surface of diseased and/or cancer cells that may be used to diagnose and treat such diseases and/or cancers with antibodies and other agents which specifically recognize targets on the surface of cells. It is an object of this invention to identify targets on the surface of diseased and/or cancer cells that are limited in expression on normal tissues and cells. PIPA is such a target. It is another objective to provide novel compounds for use in the assay of PIPA, and for use as immunogens or for selecting anti-human PIPA antibodies.
As will be described in more detail below, the present inventors have discovered a novel antigen, which we refer to herein as PIPA, identified as the antigen target of the novel antagonists, modulators and antibodies provided herein.